linux-kernel - Re: [PATCH] powerpc/64s: Fix possible corruption on big endian due to pgd/pud

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Message-ID: <87bm3add9f.fsf@concordia.ellerman.id.au>
Date:   Sun, 17 Feb 2019 19:34:36 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Segher Boessenkool <segher@...nel.crashing.org>,
        Balbir Singh <bsingharora@...il.com>
Cc:     erhard_f@...lbox.org, jack@...e.cz, linuxppc-dev@...abs.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [PATCH] powerpc/64s: Fix possible corruption on big endian due to pgd/pud_present()

Segher Boessenkool <segher@...nel.crashing.org> writes:

> Hi all,
>
> On Sat, Feb 16, 2019 at 09:55:11PM +1100, Balbir Singh wrote:
>> On Thu, Feb 14, 2019 at 05:23:39PM +1100, Michael Ellerman wrote:
>> > In v4.20 we changed our pgd/pud_present() to check for _PAGE_PRESENT
>> > rather than just checking that the value is non-zero, e.g.:
>> > 
>> >   static inline int pgd_present(pgd_t pgd)
>> >   {
>> >  -       return !pgd_none(pgd);
>> >  +       return (pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT));
>> >   }
>> > 
>> > Unfortunately this is broken on big endian, as the result of the
>> > bitwise && is truncated to int, which is always zero because
>
> (Bitwise "&" of course).

Thanks, I fixed that up.

cheers